Measurement of the electroweak production of dijets in association with a $Z$-boson and distributions sensitive to vector boson fusion in proton-proton collisions at $\sqrt{s}=8$ TeV using the ATLAS detector
Measurements of fiducial cross sections for the electroweak production of two jets in association with a Z-boson are presented. The measurements are performed using 20.3 fb$^{-1}$ of proton-proton collision data collected at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV by the ATLAS experiment at the Large Hadron Collider. The electroweak component is extracted by a fit to the dijet invariant mass distribution in a fiducial region chosen to enhance the electroweak contribution over the dominant background in which the jets are produced via the strong interaction. The electroweak cross sections measured in two fiducial regions are in good agreement with the Standard Model expectations and the background-only hypothesis is rejected with significance above the 5$\sigma$ level. The electroweak process includes the vector boson fusion production of a Z-boson and the data are used to place limits on anomalous triple gauge boson couplings. In addition, measurements of cross sections and differential distributions for inclusive Z-boson-plus-dijet production are performed in five fiducial regions, each with different sensitivity to the electroweak contribution. The results are corrected for detector effects and compared to predictions from the Sherpa and Powheg event generators.
30 January 2014
Contact: Standard Model conveners
internal
e-print arXiv:1401.7610 - pdf from arXiv - Physics Briefing
Figures
Figure 01a
Representative leading-order Feynman diagrams for electroweak Zjj production at the LHC: (a) vector boson fusion (b) Z-boson bremsstrahlung and (c) non-resonant l+l-jj production.
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Figure 01b
Representative leading-order Feynman diagrams for electroweak Zjj production at the LHC: (a) vector boson fusion (b) Z-boson bremsstrahlung and (c) non-resonant l+l-jj production.
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Figure 01c
Representative leading-order Feynman diagrams for electroweak Zjj production at the LHC: (a) vector boson fusion (b) Z-boson bremsstrahlung and (c) non-resonant l+l-jj production.
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Figure 02a
Examples of leading-order Feynman diagrams for (a) strong Zjj production and (b) diboson-initiated Zjj production.
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Figure 02b
Examples of leading-order Feynman diagrams for (a) strong Zjj production and (b) diboson-initiated Zjj production.
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Figure 03a
Comparison of data and simulation in the baseline region for (a,b) the leading jet transverse momentum and rapidity, (c,d) the subleading jet transverse momentum and rapidity, (e,f) the invariant mass and rapidity span of the dijet system. The simulated samples are normalised to the cross-section predictions and then stacked. The error bars reflect the statistical uncertainties of the data. The hatched band in the ratio reflects the total experimental systematic uncertainty on the simulation.
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Figure 03b
Comparison of data and simulation in the baseline region for (a,b) the leading jet transverse momentum and rapidity, (c,d) the subleading jet transverse momentum and rapidity, (e,f) the invariant mass and rapidity span of the dijet system. The simulated samples are normalised to the cross-section predictions and then stacked. The error bars reflect the statistical uncertainties of the data. The hatched band in the ratio reflects the total experimental systematic uncertainty on the simulation.
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Figure 03c
Comparison of data and simulation in the baseline region for (a,b) the leading jet transverse momentum and rapidity, (c,d) the subleading jet transverse momentum and rapidity, (e,f) the invariant mass and rapidity span of the dijet system. The simulated samples are normalised to the cross-section predictions and then stacked. The error bars reflect the statistical uncertainties of the data. The hatched band in the ratio reflects the total experimental systematic uncertainty on the simulation.
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Figure 03d
Comparison of data and simulation in the baseline region for (a,b) the leading jet transverse momentum and rapidity, (c,d) the subleading jet transverse momentum and rapidity, (e,f) the invariant mass and rapidity span of the dijet system. The simulated samples are normalised to the cross-section predictions and then stacked. The error bars reflect the statistical uncertainties of the data. The hatched band in the ratio reflects the total experimental systematic uncertainty on the simulation.
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Figure 03e
Comparison of data and simulation in the baseline region for (a,b) the leading jet transverse momentum and rapidity, (c,d) the subleading jet transverse momentum and rapidity, (e,f) the invariant mass and rapidity span of the dijet system. The simulated samples are normalised to the cross-section predictions and then stacked. The error bars reflect the statistical uncertainties of the data. The hatched band in the ratio reflects the total experimental systematic uncertainty on the simulation.
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Figure 03f
Comparison of data and simulation in the baseline region for (a,b) the leading jet transverse momentum and rapidity, (c,d) the subleading jet transverse momentum and rapidity, (e,f) the invariant mass and rapidity span of the dijet system. The simulated samples are normalised to the cross-section predictions and then stacked. The error bars reflect the statistical uncertainties of the data. The hatched band in the ratio reflects the total experimental systematic uncertainty on the simulation.
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Figure 04
Fiducial cross-section measurements for inclusive Zjj production in the l+l- decay channel, compared to the POWHEG prediction for strong and electroweak Zjj production and the small contribution from diboson initiated Zjj production predicted by SHERPA. The (black) circles represent the data and the associated error bar is the total uncertainty in the measurement. The (red) triangles represent the theoretical prediction, the associated error bar (or hatched band in the lower plot) is the total theoretical uncertainty on the prediction.
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Figure 05a
Example systematic uncertainty breakdown for (a) the normalised differential cross section and (b) the jet veto efficiency, as a function of the rapidity separation of the two leading jets in the baseline region. The effect of MC statistics, pileup modelling and JVF modelling are combined into one uncertainty labelled `other'.
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Figure 05b
Example systematic uncertainty breakdown for (a) the normalised differential cross section and (b) the jet veto efficiency, as a function of the rapidity separation of the two leading jets in the baseline region. The effect of MC statistics, pileup modelling and JVF modelling are combined into one uncertainty labelled `other'.
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Figure 06a
Unfolded normalised differential cross section distribution as a function of dijet invariant mass in (a) the baseline and (b) the search regions. The data are shown as filled (black) circles. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 06b
Unfolded normalised differential cross section distribution as a function of dijet invariant mass in (a) the baseline and (b) the search regions. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 07a
Unfolded normalised differential cross section distribution as a function of the rapidity separation between the leading jets in (a) the baseline and (b) the search regions. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 07b
Unfolded normalised differential cross section distribution as a function of the rapidity separation between the leading jets in (a) the baseline and (b) the search regions. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 08a
Unfolded normalised differential cross section distribution as a function of the number of jets in the rapidity interval between the two leading jets in the high mass region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 08b
Unfolded normalised differential cross section distribution as a function of the azimuthal angle between the two leading jets in the high mass region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 08c
Unfolded normalised differential cross section distribution as a function of the normalised transverse momentum balance in the high mass region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 09a
Unfolded jet veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets. Unfolded average number of jets in the rapidity interval between the two leading jets as a function of the dijet invariant mass and (d) the rapidity separation between the two leading jets. All distributions are measured in the baseline region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 09b
Unfolded jet veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets. Unfolded average number of jets in the rapidity interval between the two leading jets as a function of the dijet invariant mass and (d) the rapidity separation between the two leading jets. All distributions are measured in the baseline region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 09c
Unfolded jet veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets. Unfolded average number of jets in the rapidity interval between the two leading jets as a function of the dijet invariant mass and (d) the rapidity separation between the two leading jets. All distributions are measured in the baseline region.
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Figure 09d
Unfolded jet veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets. Unfolded average number of jets in the rapidity interval between the two leading jets as a function of the dijet invariant mass and (d) the rapidity separation between the two leading jets. All distributions are measured in the baseline region.
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Figure 10a
Unfolded transverse momentum balance veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets, in the baseline region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 10b
Unfolded transverse momentum balance veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets, in the baseline region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 11a
The dijet invariant mass distribution in the control region. The simulation has been normalised to match the number of events observed in the data. The lower panel shows the reweighting function used to constrain the shape of the background template. (b) The dijet invariant mass distribution in the search region. The signal and (constrained) background templates are scaled to match the number of events obtained in the fit. The lowest panel shows the ratio of constrained and unconstrained background templates to the data.
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Figure 11b
The dijet invariant mass distribution in the control region. The simulation has been normalised to match the number of events observed in the data. The lower panel shows the reweighting function used to constrain the shape of the background template. (b) The dijet invariant mass distribution in the search region. The signal and (constrained) background templates are scaled to match the number of events obtained in the fit. The lowest panel shows the ratio of constrained and unconstrained background templates to the data.
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Figure 12a
(a) Background reweighting functions obtained for different choices of control region. (b) The agreement between data and simulation in the 25 < pt < 38 GeV subregion both before and after applying a background reweighting function derived in the pt > 38 GeV subregion.
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Figure 12b
(a) Background reweighting functions obtained for different choices of control region. (b) The agreement between data and simulation in the 25 < pt < 38 GeV subregion both before and after applying a background reweighting function derived in the pt > 38 GeV subregion.
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Auxiliary material
Figure 01a
Unfolded normalised differential cross section distribution as a function of dijet invariant mass in (a) the high-pt and (b) the control regions. The data are shown as filled (black) circles. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 01b
Unfolded normalised differential cross section distribution as a function of dijet invariant mass in (a) the high-pt and (b) the control regions. The data are shown as filled (black) circles. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 02a
Unfolded normalised differential cross section distribution as a function of the rapidity separation between the leading jets in (a) the high-pt and (b) the control regions. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 02b
Unfolded normalised differential cross section distribution as a function of the rapidity separation between the leading jets in (a) the high-pt and (b) the control regions. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 03a
Unfolded jet veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets. Unfolded average number of jets in the rapidity interval between the two leading jets as a function of the dijet invariant mass and (d) the rapidity separation between the two leading jets. All distributions are measured in the high-pt region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 03b
Unfolded jet veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets. Unfolded average number of jets in the rapidity interval between the two leading jets as a function of the dijet invariant mass and (d) the rapidity separation between the two leading jets. All distributions are measured in the high-pt region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 03c
Unfolded jet veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets. Unfolded average number of jets in the rapidity interval between the two leading jets as a function of the dijet invariant mass and (d) the rapidity separation between the two leading jets. All distributions are measured in the high-pt region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 03d
Unfolded jet veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets. Unfolded average number of jets in the rapidity interval between the two leading jets as a function of the dijet invariant mass and (d) the rapidity separation between the two leading jets. All distributions are measured in the high-pt region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 04a
Unfolded transverse momentum balance veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets, in the high-pt region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 04b
Unfolded transverse momentum balance veto efficiency as a function of (a) the dijet invariant mass and (b) the rapidity separation between the two leading jets, in the high-pt region. The vertical error bars show the size of the total uncertainty on the measurement, with tick marks used to reflect the size of the statistical uncertainty only. Particle-level predictions from SHERPA and POWHEG are shown for combined strong and electroweak Zjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, around the central prediction, which is shown as a solid line. The predictions from SHERPA and POWHEG for strong Zjj production (labelled QCD) are shown as dashed lines.
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Figure 05a
(a,b) Particle-level shape comparisons of the rapidity separation between the two leading jets and the dijet invariant mass distribution in the baseline region for the electroweak Zjj signal and the background, which includes QCD Zjj, diboson and top-antitop production. (c,d) Particle-level shape comparisons of the number of jets in the rapidity interval bounded by the dijet system and the normalised transverse momentum balance distributions for the electroweak Zjj signal and the background. All curves are normalised to unit area.
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Figure 05b
(a,b) Particle-level shape comparisons of the rapidity separation between the two leading jets and the dijet invariant mass distribution in the baseline region for the electroweak Zjj signal and the background, which includes QCD Zjj, diboson and top-antitop production. (c,d) Particle-level shape comparisons of the number of jets in the rapidity interval bounded by the dijet system and the normalised transverse momentum balance distributions for the electroweak Zjj signal and the background. All curves are normalised to unit area.
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Figure 05c
(a,b) Particle-level shape comparisons of the rapidity separation between the two leading jets and the dijet invariant mass distribution in the baseline region for the electroweak Zjj signal and the background, which includes QCD Zjj, diboson and top-antitop production. (c,d) Particle-level shape comparisons of the number of jets in the rapidity interval bounded by the dijet system and the normalised transverse momentum balance distributions for the electroweak Zjj signal and the background. All curves are normalised to unit area.
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Figure 05d
(a,b) Particle-level shape comparisons of the rapidity separation between the two leading jets and the dijet invariant mass distribution in the baseline region for the electroweak Zjj signal and the background, which includes QCD Zjj, diboson and top-antitop production. (c,d) Particle-level shape comparisons of the number of jets in the rapidity interval bounded by the dijet system and the normalised transverse momentum balance distributions for the electroweak Zjj signal and the background. All curves are normalised to unit area.
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Figure 06a
(a) Statistical correlations between the distributions for the unfolded dijet invariant mass and the rapidity separation between the two leading jets (both in the baseline region). (b) Statistical correlations between the distributions for the average number of jets in the rapidity interval bounded by the dijet system and the normalised transverse momentum balance (both in the high-mass region).
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Figure 06b
(a) Statistical correlations between the distributions for the unfolded dijet invariant mass and the rapidity separation between the two leading jets (both in the baseline region). (b) Statistical correlations between the distributions for the average number of jets in the rapidity interval bounded by the dijet system and the normalised transverse momentum balance (both in the high-mass region).
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